This invention relates to the fusing of toner images and more particularly to a toner image fuser that provides a well controlled and safe energy source which eliminatesthe need for standby power.
In the art of xerography or other similar image creation arts, a latent electrostatic image is formed on a charge-retentive surface which may comprise a photoconductor which generally comprises a photoconductive insulating material adhered to a conductive backing. When the image is formed on a photoconductor, the photoconductor is first provided with a uniform charge after which it is exposed to a light image of an original document to be reproduced. The latent electrostatic images, thus formed, are rendered visible by applying any one of numerous pigmented resins specifically designed for this purpose.
It should be understood that for the purposes of the present invention, which relates to rendering permanent powder or toner images, the latent electrostatic image may be formed by means other than by the exposure of an electrostatically charged photosensitive member to a light image of an original document. For example, the latent electrostatic image may be generated from information electronically stored or generated, and the digital information may be converted to alphanumeric images by image generation electronics and optics. However, such image generation electronic and optic devices form no part of the present invention.
In the case of a reusable photoconductive surface, the pigmented resin, more commonly referred to as toner, which forms the visible images is transferred to a substrate such as plain paper. After transfer the images are made to adhere to the substrate using a fuser apparatus.
To date, the use of simultaneous heat and contact pressure using a pair of nip forming rollers for fusing toner images has been the most widely accepted commercially. Heretofore, it has been necessary with the foregoing type of fuser to heat the fuser roll or rolls not only when images are being fused but also during standby when images are not being fused. This is because of the long delay that would be required to elevate the fuser to a proper operating temperature if the heat supply were turned off during standby, the long delay being due to the relatively large mass that has to be brought up to the fusing temperature. Moreover, the need for the use of standby power dissipation renders such fusers thermally inefficient. Such delays would not be tolerated by the user even though operating the fuser in such a manner would eliminate a substantial waste of energy and reduce the effect thereof on ambient conditions.
Elimination of fuser standby power has been accomplished in prior art devices such as flash fusers and cold pressure fusers. Both of these types of fusers, however, exhibit other drawbacks. For example, cold pressure fusers exhibit poor quality images. Flash fusers create undesirable effluents and they work very poorly with colored toners, especially the lighter colored ones. Also, the optical density of flash fused images is considered unsatisfactory.
In addition to the aftermentioned types of fusers designed to obviate the problems noted, "instant on" fusers such as disclosed in U.S. Pat. No. 4,565,439 granted to Scott D. Reynolds on Jan. 21, 1986 have been contemplated. As disclosed therein, that fuser comprises a low mass belt heated by an external heatsource positioned remotely from a fuser nip through which substrates carrying toner images are passed.
Accordingly, we have provided, as disclosed herein, a fuser that exhibits high thermal efficiency and that can be satisfactorily operated without the employment of standby power. To this end, an acoustic transducer in the form of an ultrasonic welding horn is employed.
Ultrasonic welding and other types of vibrating devices have been disclosed for use in different applications or functions in connection with xerographic imaging. For example, such devices have been used for the transfer and development of toner images as well as residual toner removal from a charge retentive surface. Examples of their use in the transfer and development of toner images and the removal of residual toner particles can be found in the following patents:
U.S. Pat. No. 5,210,577 granted to William J. Nowak on May 11, 1993 discloses an imaging device including a non-rigid member with a charge retentive surface moving along an endless path, an arrangement for creating a latent image on the charge retentive surface, a developer to develop the latent image with toner, a transfer arrangement electrostatically transferring the developed toner image to a copy sheet, and a resonator for enhancing toner release from the charge retentive surface, producing relatively high frequency vibratory energy and having a portion adapted for contact across the non-rigid member, generally transverse to the direction of movement of the non-rigid member.
Union of Soviet Socialist Republic Patent No. 301679 published on Apr. 21, 1969 in the name of Steshets et al discloses a roll for fusing toner images which roll is an annular vibrator fabricated from magnetostrictive material (e.g. nickel, barium, titanium, etc.) with a wind situated in such a way that the vibrator emits vibrations radially. At the points of contact, significant pressure and acceleration are developed so that the abrasive magnetographic developer is easily forced into the paper.
French Publication No. 2 280 115 based on Patent Application No. 75 22768 filed on Jul. 22, 1975 discloses a transfix apparatus wherein surfaces placed in mutual contact are subjected to ultrasonic vibrations.
U.S. Pat. No. 5,081,500 granted to Christopher Snelling on Jan. 14, 1992 discloses a method and apparatus for using vibratory energy to reduce transfer deletions in electrophotographic imaging . At a transfer station, a resonator suitable for generating vibratory energy is arranged in line contact with the back side of the charge retentive surface, to uniformly apply vibratory energy to the charge retentive member. Toner is released from the electrostatic and mechanical forces adhering it to the charge retentive surface at the line contact position. In those areas of the latent image characterized by non-intimate contact of the sheet with the charge retentive surface, toner is transferred across the gap by the electrostatic transfer process, despite the fact that the charge on the paper would not normally be sufficient to attract toner to the sheet from the charge retentive surface.
U.S. Pat. No. 4,111,546 to Maret proposes to enhance residual toner removal from an imaging surface by applying high frequency vibratory energy to an imaging surface with a vibratory member, coupled to an imaging surface at the cleaning station. The vibratory member described is a horn arrangement excited with a piezoelectric transducer (Piezoelectric element) at a frequency in the range of about 20 kilohertz.
U.S. Pat. No. 4,684,242 to Schultz describes a cleaning apparatus that provides a magnetically permeable cleaning fluid held within a cleaning chamber, wherein an ultrasonic horn driven by piezoelectric transducer element is coupled to the backside of the imaging surface to vibrate the fluid within the chamber for enhanced cleaning.
U.S. Pat. No. 4,007,982 to Stange provides a cleaning blade with an edge vibrated at a frequency to substantially reduce the frictional resistance between the blade edge and the imaging surface, preferably at ultrasonic frequencies.
U.S. Pat. No. 4,121,947 to Hemphill provides an arrangement which vibrates a photoreceptor to dislodge toner particles by entraining the photoreceptor about a roller, while rotating the roller about an eccentric axis.
Xerox Disclosure Journal "Floating Diaphragm Vacuum Shoe", by Hull et al., Vol. 2, No. 6, November/December 1977 shows a vacuum cleaning shoe wherein a diaphragm is oscillated in the ultrasonic range.
U.S. Pat. No. 3,653,758 to Trimmer et al suggests that transfer of toner from an imaging surface to a substrate in a non contacting transfer electrostatic printing device may be enhanced by applying vibratory energy to the backside of an imaging surface at the transfer station.
U.S. Pat. No. 4,546,722 to Toda et al., U.S. Pat. No. 4,794,878 to Connors et al., and U.S. Pat. No. 4,833,503 to Snelling disclose use of a piezoelectric transducer driving a resonator for the enhancement of development within a developer housing.
Japanese Published Patent Application. 62-195685 suggests that imagewise transfer of photoconductive toner, discharged in imagewise fashion, from a toner retaining surface to a substrate in a printing device may be enhanced by applying vibratory energy to the backside of the toner retaining surface.
U.S. Pat. No. 3,854,974 to Sato et al. discloses vibration simultaneous with transfer across pressure engaged surfaces.
Resonators for applying vibrational energy to some other member are known, for example in U.S. Pat. No. 4,363,992 to Holze, Jr. which shows a horn for a resonator, coupled with a piezoelectric transducer device supplying vibrational energy, and provided with slots partially through the horn for improving non uniform response along the tip of the horn. U.S. Pat. No. 3,113,225 to Kleesattel et al. describes an arrangement wherein an ultrasonic resonator is used for a variety of purposes, including aiding in coating paper, glossing or compacting paper and as friction free guides. U.S. Pat. No. 3,733,238 to Long et al. shows an ultrasonic welding device with a stepped horn. U.S. Pat. No. 3,713,987 to Low shows ultrasonic agitation of a surface, and subsequent vacuum removal of released matter.
Coupling of vibrational energy to a surface has been considered in Defensive Publication T893,001 by Fisler which shows an ultrasonic energy creating device arranged in association with a cleaning arrangement in a xerographic device, and coupled to the imaging surface via a bead of liquid through which the imaging surface is moved. U.S. Pat. No. 3,635,762 to Ott et al. and U.S. Pat. No. 3,422,479 to Jeffee show a similar arrangement where a web of photographic material is moved through a pool of solvent liquid in which an ultrasonic energy producing device is provided. U.S. Pat. No. 4,483,034 to Ensminger shows cleaning of a xerographic drum by submersion into a pool of liquid provided with an ultrasonic energy producing device.
U.S. Pat. No. 3,190,793 Starke shows a method of cleaning paper making machine felts by directing ultrasonic energy through a cleaning liquid in which the felts are immersed.
U.S. Pat. No. 4,879,564 granted to Michael E. Long on Nov. 7, 1989 relates to the use of ultrasonic energy to heat a dye image in a receiverto cause such dye to fuse into the receiver.
U.S. Pat. No. 5,010,369 granted to Nowak et al on Apr. 23, 1991 relates to an electrophotographic device of the type including a flexible belt charge retentive member, driven along an endless path through a series of processing stations that create a latent image on the charge retentive surface, develop the image with toner, and bring a sheet of paper or other transfer member into intimate contact with the charge retentive surface at a transfer station for electrostatic transfer of toner from the charge retentive surface to the sheet. For the enhancement of toner release from a surface at any of the processing stations, a resonator suitable for generating vibratory energy is arranged in line contact with the back side of the charge retentive surface, to uniformly apply vibratory energy to the charge retentive member. The resonator includes a horn, a continuous support member, and a continuous vibration producing member that drives the horn at a resonant frequency to apply vibratory energy to the belt. The horn includes a platform or base portion, a horn portion extending therefrom, and having a contacting tip. The horn is segmented, through the contacting tip to the platform portion, into a plurality of elements which each act more or less individually. In alternative embodiments, the vibration producing member that drives the horn, and/or the support member may also be segmented in a corresponding manner.
U.S. patent application Ser. No. 08/157599 assigned to the same assignee as t application relates to an ultrasonic fuser for fixing toner images to substrates which utilizes an acoustic transducer or resonator in the form of an ultrasonic welding horn and a viscoelastic member. As toner images carried on a substrate are moved between the resonator and the viscoelastic member heat energy is created both in the toner particles forming the images and the viscoelastic member. The heat energy created in the viscoelastic member is transferred to the toner images through intimate contact therewith and together with the heat generated in the toner serves to elevate the toner to its fusing temperature.
All the references cited herein are specifically incorporated by reference for their teachings.